The cured in place method of lining damaged or broken pipes, such as sewers and gas pipes, has become a very successful method of repairing underground pipes. The method avoids the need to excavate the underground pipe and the resulting damage to surface infrastructure, such as paved streets and buildings. The cured in place method involves first positioning the liner inside the pipe while the liner is in a flexible state, then curing the liner to a hard state within the pipe while forcing the liner against the inside of the damaged pipe. Previous methods use air or water to pressurize the liner to have the flexible liner conform to the inside of the pipe and cure the liner to a hard state while it is held by the pressure to the inside of the pipe.
The prior art liners have been made by using a fabric on one side of the liner and a polymer sheet on the other side. The fabric is saturated with an uncured thermoset material. The curing, that is the process of converting the thermoset material to a rigid state, is performed after the liner has been placed inside the pipe. The liner can be placed in the pipe to be repaired by either the dragged-in method as described in U.S. Pat. No. 4,009,063 or the inversion method as described in U.S. Pat. No. 4,064,211, both of these patents are herein incorporated by reference. The polymer sheet placed on the fabric must be resistant to the thermosetting material used and also able to withstand the heat used to cure the thermoset material. Various thermoplastics and elastomers have been used to coat the fabrics, with polyurethane being frequently used.
Thermoplastic polyurethane is particularly desirable because of its abrasion resistance, tear resistance and elastic properties. However, recent installers of pipe liners expressed a desire to use an epoxy resin with an amine curative as the thermoset material in the liner and to use steam rather than hot water to initiate the cure and to press the liner against the inside of the pipe. The use of epoxy resins has some environmental benefits for the installer and steam is faster to evacuate from the inflated liner than is hot water.
The thermoplastic polyurethanes (TPU) used before in pipe liner are not acceptable when epoxy resin with an amine curative is used to saturate the non-woven fabric and steam is used to install the liner. The epoxy/amine reaction is exothermic and the heat from this reaction and the steam will cause prior art TPU to blow through the fabric containing the epoxy resin and form holes in the liner.
It can be beneficial to have a TPU which could be used in a cured in place liner where epoxy resin with an amine curative is used and where steam is used to install the liner. It would also be beneficial to have a TPU which could be used in a cured in place liner with either steam or hot water being used to cure the thermoset resin and where the thermoset resin can be epoxy, vinyl ester resin or polyester resin.